1. Field of the Invention
The present invention relates to oxidative dehydrogenation catalysts, and more particularly to crystalline silica oxidative dehydrogenation catalysts which are useful for producing diolefins from C.sub.4 to C.sub.8 mono-olefins.
2. The Prior Art
The use of dehydrogenation catalysts to oxidize hydrocarbons to diolefins is known and appreciated by the prior art. For example, U.S. Pat. No. 3,927,138 relates to a process for producing diolefins from paraffins, especially the dehydrogenation of butane to butenes and butadiene, using an oxidation catalyst consisting of a ferrous metal, tin, phosphorus and an alkali metal. The catalysts may be supported on or diluted with materials such as silica, alumina, boria, etc.
U.S. Pat. No. 3,914,332 discloses a process for the oxidative dehydrogenation of butane to a mixture of butenes and butadiene using a vanadium-potassium-sulfur catalyst supported on silica, which permits the use of high space velocities.
U.S. Pat. No. 3,856,881 relates to a process for the dehydrogenation of C.sub.4 and C.sub.5 hydrocarbons to produce the corresponding dehydrogenated compounds. The dehydrogenation catalyst used consists of a crystalline spinel of a phosphorus and divalent-metallic vanadium compound. Catalyst carriers such as alumina, pumice, silicon, etc. are additionally described as suitable for use in the dehydrogenation catalyst.
U.S. Pat. No. 3,789,078 discloses a dehydrogenation process and dehydrogenation catalysts which are useful for oxidatively dehydrogenating organic compounds such as alkenes, alkadienes, cycloalkenes, alkylpyidines and alkyl aromatics. The catalyst consists of a combination of phosphorus, tin and a Group IA or IIA metal of the Periodic Table. Substantially any phosphorus, tin and Group IA or IIA containing materials may be employed in the catalyst so long as at least one of the materials used contains oxygen.
U.S. Pat. No. 3,775,508 relates to an oxidative dehydrogenation process for dehydrogenating C.sub.2 to C.sub.10 alkenes, alkadienes, etc. using an oxidation catalyst consisting of phosphorus, tin and a Group IA or IIA metal of the Periodic Table. The catalyst is improved by including a heat-volatile activity-stimulating ammonium salt in the catalyst composition prior to the catalyst particle-forming stage.
As can readily be determined from the above, there is an ongoing effort to develop oxidative dehydrogenation catalysts for producing diolefins from alkanes and mono-olefins.
Accordingly, it is an object of the present invention to provide an oxidative dehydrogenation catalyst for producing diolefins from mono-olefins.
Another object of the present invention is to provide an oxidative dehydrogenation catalyst having a large surface area which is useful for producing butadiene and to provide a method of preparing the same.
A further object of the present invention is to provide a method for obtaining improved yields and selectivity of diolefins, for example, butadiene.
These and other objects are accomplished according to the present invention by oxidizing a C.sub.4 to C.sub.8 mono-olefin to the corresponding diolefin in the presence of an alkali metal promoted oxidative dehydrogenation catalyst comprising the oxides of an alkali metal, vanadium, phosphorus and tin on a crystalline silica support.